How to render over camera border or overscan?
There is currently no builtin way to correctly setup an overscan. However you can simply use the workaround Andrew Price mention in his twitter feed from 2015.


  In the render dimensions set to 105%. Then with the camera selected, go to focal length, click edit, add *0.95 to end of whatever is current.


To add 20% to the image:


Go to the render dimensions and enter 120% under the Resolution section.

Then click into the focal length field of the camera and divide the current focal length by 1.2



This obviously won't produce a true overscan, like an .exr image supports. You'll have to add a Reformat node (centered) in Nuke manually.